Objective : Curved walking has been reported as one of the most difficulty activities for stroke patients. Muscle synergy is defined as functional units of the CNS that coordinate the co-activation of different muscle groups. The purpose of this study was to compare muscle synergy in the affected leg of stroke patients with age-matched controls during curved walking.

Interventions : Participants walked on the circle with 1.2meter radius at self-selected speed in randomly ordered walking directions; 1) the affected leg placed in the inner side and 2) outer side. All sEMG signals were recorded unilaterally from either the affected leg of the stroke patients or the dominant leg of the healthy subjects.

Main Outcome Measure(s) : Muscle synergies were extracted from sEMG signals using a non-negative matrix factorization (NNMF) algorithm. The optimal number of synergies has been defined as the minimum number needed to obtain variability accounted for (VAF) > 90%.

Results : Stroke subjects showed fewer muscle synergies in walking when affected leg placed in inner side than outer side (3.48±0.52, 4.62±0.64, P=.032, respectively). There was no difference in the number of muscle synergy in healthy participants between two walking directions (4.22±0.64, 4.38±0.52, P=.321, respectively).

Conclusions : Insufficient muscle activation in posterior leg muscles may contribute to the reduced synergy number in walking when the affected leg placed in inner side. These findings provide a clinical strategy to rehabilitate the walking ability of stroke patients in curved path.